Machine for working rubber and like plastics



MACHINE FOR WORKING RUBBER AND LIKE PLASTICS Filed April 2l, 1967 J. D.WEIR .lune l?, 1969 Sheet R. w m I E M S E@ WMU Hume l?, m9 J. D. wl-:IR

MACHINE FOR WORKING RUBBER AND LIKE PLASTICS sheet afs Filed April 21,1967 aff/w55 o a5/e l BY f wmf/5MM' A7' To@ NE ys.

June 17, 1969 J. D. wElR 3,449,793

MACHINE FOR WORKING RUBBER AND LIKE PLASTICS l Filed April 21. 1967sheet 3 of s 1N VEN TOR. 044,445.5 0. M5/,Q

A TTOIVE YS United States Patent O "ice 3,449,793 MACHINE FOR WORKINGRUBBER AND LIKE PLASTICS `lames D. Weir, Anchorage, Ky., assignor toInternational Rubber Industries, Inc., Louisville, Ky.

Filed Apr. 21, 1967, Ser. No. 632,812

Int. Cl. B01f 7/08 U.S. Cl. 18-12 9 Claims ABSTRACT F THE DISCLOSURE Amachine for Working plastics in a continuous operation, and having ahollow cylinder with a feed inlet at one end and a delivery outlet atthe other, a `screw rotatably mounted in the cylinder and havingfeeding, masticating and delivery sections disposed sequentiallytherealong, said screw having at least one thread whose pitch varies soas to increase fand decrease within the length of the masticatingsection to define with said cylinder a plastic ow channel whosecross-sectional area increases and decreases. Desirably, a pair ofgrooves of varying depth is provided at the root of the thread, onegroove on each side, the depth of the first groove increasing as that ofthe second decreases causing the plastic to shift laterally across thechannel as it ows around and progresses axially forwardly along thescrew. Each of said grooves preferably both increases and decreases indepth within the length of the masticating section. Desirably, anadditional thread is formed on the screw for the entire length of themasticating section, said additional thread having either a constantpitch or a varying pitch. When two or more threads are provided, a pairof grooves is formed at the root of each thread so that the two groovesin the channel formed between the two threads will alternately increaseand decrease in depth as the thread progresses along the screw.

This invention relates to machines for working (including mixing,masticating, plastifying and preheating) rubber and rubber-like plasticsand compositions formed thereof, and more particularly to 4improvementsin the feed screw theerof, as for example, the screw of a coldfeedextruder.

It is, of course, well known in the art to provide various forms of feedscrews in extruders according to the type of plastic -rnaterial which isbeing worked. Generally, such screws have a feeding section leading to amasticating section and culminate in a delivery section at the mouth ofthe extruder. In the masticating section, with which this invention isprimarily concerned, it is known to employ a thread, or flight, having aconstant pitch, but in which the root diameter is progressivelydecreased so that the channel defined between axially spaced portions ofthe thread and the enclosing cylinder of the screw is progressivelydecreased in height, or radially of the screw, as the thread progressesaround and axially forward along the screw. Such a constructionprogressively squeezes the plastic material more and more as itapproaches the delivery section, thus providing a squeezing in onedirection, i.e., radially of the screw.

It is also known to provide extruder screws formed with a double threadof different, but constant pitch whereby to change the width of thechannel formed between the two threads, thereby squeezing the plasticlongitudinally of the channel as it progresses axially along 'the screw.In some instances it has been suggested that the root diameter betweenthe double threads be .both increased and decreased7 thereby imparting asuccessive expansion and squeezing, or contraction, of the plastic3,449,793 Patented June 17, 1969 in the radial direction as it movesalong the channel due to rotation of the screw.

It is a principal object of the present invention to provide animprovement in the construction of the masticating sections ofconventional feed screws whereby the channel along which the plastic ismoved is so shaped as to alternately squeeze and expand the plastic ineach of three directions perpendicular to each other, i.e.,longitudinally, laterally, and vertically of the channel, to therebyincrease the efficiency of the mixing, plastifying, masticating andheating of the plastic components. The longitudinal squeezing andexpanding is obtained by providing the `channel walls in the form of athread having a constantly varying pitch so that the walls progressivelyapproach each other and spread apart. The lateral squeezing andexpansion is obtained by providing a pair of grooves at opposite sidesof the channel adjacent the thread walls and which vary in depth, onegroove increasing when the other `decreases in depth. This presses theplastic from the shallower groove to t-he deeper groove across thechannel. The radial squeezing and expanding of the plastic is caused bythe bottom walls of said grooves which vary in depth, and change thevertical height of the channel. In addition, if desired, the rootdiameter of the screw thread may vary preferably in a manner generallyinverse to the width of the thread, or to the channel between threa-ds.

It is another object of the invention to provide an irnproved screwassembly having the above described characteristics, so constructed asto be capable of performing on a continuous basis the functions of anintensive internal mixer, a mixing rnill, and a warm-up mill, as well asa conventional cold-feed extruder.

A further object of the invention is to provide an improved device,having the above described characteristics, wherein the masticatingsection of the screw is provided with a single variable pitch thread inwhich the variation is such that at any successive given point along thethread length the distance between thread portions measured axially isnot a constant.

Still another object of the invention is to provide an improved screw,having the above described characteristics, in which the masticatingportion is formed by a double thread at least-one of which varies inpitch, such variation being constant, or regular, or inconstant, orirregular.

A still further object of the invention is to provide an improved screw,having the above described characteristics, in which the masticatingportion is provided with at least two threads both of which vary inpitch.

The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together 'with additional objects and advantages thereof,will best be understood from the following description of specificembodiments when read in connection 'with the accompanying drawings,wherein like reference characters indicate like parts throughout theseveral figures `and in which:

FIG. l is a longitudinal axial section taken vertically through theimproved screw portion of an extruder according to the invention; i FIG.2 is a fragmentary enlarged sectional view, similar to that of FIG. 1,but showing only a portion of the masticating section;

FIG. 3 is a development view of a portion of'the threads in themasticating section of the screw of FIG. l;

FIG. 4 illustrates cross-sectionally the screw in various parts numbered1-10 taken successively at 90 intervals of rotation on the lines 1-10 inFIG. 2, and also in F-IG. l, the sections being rotated to place thestandard 3 pitch thread at the left and horizontally in each of the tenviews;

FIG. 5 is a fragmentary elevational vie'w of the masticating section ofa modified screw employing only one thread having a constantly varyingpitch;

FIG. 6 is an elevational view simil-ar to FIG. 5, showing anothermodification in which two threads each of variable pitch are formed inthe masticating section of the screw; and

FIG. 7 is a developmental view similar to FIG. 3 of a portion of thethreads in the masticating section of the screw of FIG. 6.

Referring now more particularly to the drawings, and -rst specificallyto FIGS. 1-4, there is shown a preferred embodiment of the improvedscrew generally indicated at 10. The screw is housed in what may be aconventional hot or cold feed extruder in the bore of a cylinder 1'2,preferably of uniform diameter. A hopper 14 is provided to feed thecomponents of the plastic to be mixed into the bore of cylinder 12 atthe beginning of the feeding section 16, legended in FIG. 1. In thissection the screw is provided with Va thread 18 which may be of constantpitch as shown, or may have an irregular or varying pitch, if desired.The thread continues through the masticating section 20 and through thedelivery section 22 to an outlet of the extruder, not shown. Desirably,the screw has an outside diameter which is very slightly smaller thanthe diameter of the bore of the cylinder 12 so that upon rotation bypower means, not shown, the mass of plastic components fed through thehopper 14 will move along the screw in the channel C passing through thefeeding, masticating and delivery sections successively in aWellrecognized manner of operation of such screws.

In the masticating section a second thread 24 is formed on the screwwhich desirably has a constantly varying pitch. Thus, between thecylinder 16, the shaft of screw 10 and axially spaced portions of thethreads 18, 24 are formed two spiral chambers C', C, FIG. 2, progressingaround the screw from the feeding section to the delivery sectionthrough which the plastic components being mixed and plastified mustpass by reason of pressure of the rotating threads.

In FIGS. 3 thread 18 appears to be straight as in the development view,the screw being rolled along the development surface. The rate of changeof pitch of thread 24, whether it is constant or interrupted, regular orirregular, and the shape of the curve, proportional to amplitude andfrequency of pitch change, is expressed by a sinusoidal curve which maybe preselected depending upon the plastic materials being worked and thenature of the resulting material desired. The sinusoidal curverepresenting thread 24 at the left of FIG. 3 has been chosen as asuitable example to illustrate that the pitch is both increased anddecreased, the increase tending to widen the channel C between threads118, 24, and the decrease tending to narrow the channel C. Thecorresponding channel C is simultaneously narrowed and widened.Desirably, at least one increase and one decrease of pitch of thread 24should be utilized in the length of the masticating section. FIG. 3illustrates two complete convolutions of the screw which represent lessthan half its length in the masticating section.

At opposite sides of the standard pitch thread 18 is formed a pair ofgrooves 26, 28, see FIGS. 2 and 4, which vary in depth as the groovesand the thread progress around the screw. A similar pair of grooves 30,32, is formed, one on each side of the non-standard pitch thread 24,these grooves also varying in depth. One groove of each pair appears inthe channels C', C for plastic flow, as indicated in FIG. 3 by the wavylines 36 representing the bottom surface of the channel C' at about 20intervals, the grooves appearing at the opposite end of each line. Itwill be aparent from examination of FIG. 3 that the grooves are shapedso that of the pair within the channel C' one groove will constantlyincrease and the other decrease in depth as the grooves progress aroundthe screw, and that once a maximum depth has been reached in one grooveit will begin to decrease when simultaneously the companion groove twillbegin to increase in depth. Thus, the height of channel C at oppositesides constantly varies in such a manner as to cause the shallow grooveat one side to push the plastic laterally of the channel toward thecompanion and deeper groove on the other side. At the same time, thevariations in the depth of the grooves cause an expansion and asqueezing vertically of the flowing plastic between the channel fioorincluding the grooves and the channel ceiling formed by the cylinder 12.

A clear visualization of the construction of the screw thus fardescribed will be obtained upon study of the sectional views of thescrew included in FIG. 4. Referring first to section No. 2 of FIG. 4,the centers of threads 18, 24 are shown as being approximately 210oounterclockwise apart. The standard pitch thread 18 has been rotatedinto the horizontal appearing at the left of the section. This view hasbeen taken on line 2 of FIG. l, where it intersects the thread at thetop of FIG. 1 so that the rotation amounts to for this particularsection. The section No. 1 shows the screw similarly rotated to placethe standard pitch thread in the same relative position, the sectionhaving been taken .along line 1 which precedes the second section by 90of rotation of the screw. In section No. 1 the thread 24 is only about150 counterclockwise from thread 18. Similarly, section No. 3 is takenon line 3 of FIG. 1, and the angular counterclockwise spacing betweenthreads 18, 24 has now increased to about 225. In section No. 4 the twothreads are approximately 200 counterclockwise apart. In section No. 5the two threads are about 260 counterclockwise apart, and in section No.6 the two threads are about 150 counterclockwise apart. The variation inangular spacing between threads in sections Nos. 2 and 6 represents onefull rotation of the screw, or 360, the two threads spreading apart andcoming closer together during said revolution by reason of the variationin pitch of thread 24. Such separation and approach continues throughsections 7-10 representing a second complete revolution of the screw andfurther revolutions will cause the pattern of section 1-10 to repeat insequence. The pair of grooves 26, 28, one on each side of thread 18, isshown to be deepest in section No. 1 and getting successively shallowerin sections 2 through 6. Starting with section 7, these grooves begintoget `deeper progressively through sections 8-10, being again deepestin section No. 1. At the same time the pair of rgrooves 30, 32, one oneach side of thread 24, are shown to be sha1-lowest in section No. 1,and starting to become deeper in section No. 2 and continuingsuccessively to become Ideeper in sections 3 through y6. When the otherpair of grooves change toward becoming deeper, the grooves 30, 32 startto become shallower, as in section 7, and progressively continue tobecome shallower through sections 8, 9 and 10, becoming shallowest againinA section No. 1. It is, therefore, seeu that the floors of thechannels C', C" between threads 18, 24 are wavy and defined by curvatureof the bottoms of the four grooves and that of the connecting screwshaft surfaces. As a result, the height of each of the two channelsvaries from side-to-side so that turning of the screw will tend to forcethe plastic components from a shallow groove portion toward and into thedeeper companion groove portion. Thus, as the threads 18, 24 approacheach other at the sides of the channels C', C and the grooves 26-32 atthe sides of the channels change in depth, pressures are exerted on theplastic owing in the channels longitudinally thereof which tend to bothsqueeze, or compress, and expand, or decompress the plastic in each ofthree directions at right angels to each other, one direction beingalong the length of the channel, the second direction being along thewidth, or laterally of the channel, and the third direction beingradially of the screw, or

vertically of the channel. The change in depth of the channels may beconsidered to be a change in the root diameters of the two threads andany Suitable way of forming the threads and grooves, such as by moldingor casting, or by machining while varying the root diameter of thethreads, may be utilized to form the screw according to the invention.

In operation, turning of the screw, feeds the plastic components as amixture into the masticating section, the continuous variation of thecross-sectional shape and area of the channels between the threadsfurther defined by the root diameter of the screw shaft and the bore ofthe cylinder, forces the mixture along the channels C', C and causes theplastic mass continually to change its shape and direction of movementas the result of the alternate squeezing and expansion in each of thethree perpendicular directions defining said channels, as explainedabove. As a result an exceedingly efficient kneadiug action upon theplastic is obtained, insuring a high measure of uniformity in theproduct delivered at the output of the delivery section. In addition tothe alternate squeezing and expansion mentioned, there are changes inflow speed of portions of the moving mass of plastic resulting from thechange in volume of various portions of the channel, as between thewidely separated portions and the closely spaced portions of the threadsand the deep grooves and the shallow grooves. Thus, channel parts ofreducing volume cause a portion of the plastic to increase its speed ofmovement, and those portions of plastic entering enlarging volumes,reduce their speed of movement. As a result, a cutting action of layers,or portions, of the plastic with respect to one another is obtainedwhich greatly improves the masticating effect of the device.Consequently, it will be seen that in processing rubber and plastics forcontinuous use, that the thorough mixing and mastication required willbe more efficiently obtained than with conventional screws. Thedelivered plastic will be more homogeneous which is important when it isconsidered that the feed arrangement for devices for this type must bemade to accommodate components or additives in the form of pellets,powders, liquids, strips or solid plastic masses which may be fed intothe hopper under pressure, gravity-feed, self-feed, or by meteringdevices.

In FIG. is illustrated the masticating section of a modi-tied screw inwhich only one thread 24 is used. However, this thread is formed with aconstantly varying pitch, or pitch angle, so that the channel C2 formedbetween longitudinally spaced portions of the thread for conveying theplastic will alternately narrow and widen in the same manner asexplained for channel C' of the embodiment of FIG. l. On each side ofthe thread 24 are formed grooves 30', 32 which, therefore, appear atopposite sides of the channel C2 and these grooves are so formed thatone decreases in depth as the other increases in depth in the samemanner as previously described for the grooves 26, 32 or 28, 30 of FIG.2.

The resulting operation of the screw of FIG. 5 is similar to that aspreviously described for the embodiment of FIG. l, in spite of the factthat a standard pitch thread has been omitted, the main diffeernce beingthat only a single channel of varying width is provided in themasticating section instead of two.

FIG. 6 illustrates still another embodiment of the masticating sectionof the screw in which again two threads 242, 243 are utilized. However,both of these threads employ constantly varying pitch. A pair of grooves262, 282 is formed on each side of thread 242 and a similar pair ofgrooves 302, 322 is formed on each side of thread 243. These two pairsof grooves are dimensioned and positioned in the same manner asdescribed for the corresponding grooves 26, 28, 30 and 32 of FIG. 2

FIG. 7 is a development view of the two threads 242,

243 of the FIG. 6 embodiment, showing that both are 0f variable pitch.As a result, the narrowing and widening of each of the channels C3, C4between the two threads are increased in amplitude, and in the resultantoperation of the screw with both threads varying in patch an increasedeffect of mixing, masticating and plastifying, as well as heatingengendered by increased friction, is obtained.

Although certain specific embodiments of the invention have been shownand described, it is obvious that many modifications thereof arepossible. The invention, therefore, is not to be restricted exceptinsofar fas is necessitated by the prior art and by the spirit of theappended claims.

What is claimed is:

1. A machine for working plastics in a continuous operation, comprisinga cylinder having a uniform diameter bore, an inlet at one end and anoutlet at the other end, a screw rotatably mounted in said cylinder boreand having a feeding section, a masticating section and a deliverysection, said screw having in its masticating section at least onethread whose pitch varies, increasing and decreasing within the lengthof said masticating section to define with said cylinder a plastic owchannel whose cross-sectional area increases and decreases.

2. A machine according to claim 1 wherein a pair of grooves of varyingdepth is provided at the root of said thread one on each side, the depthof the rst groove increasing as the depth of the second decreaseswhereby to shift the plastic laterally across said channel as it flowsaround and progresses axially forward along the screw.

3. A machine according to claim 2 wherein each of said grooves bothincreases and decreases in depth within the length of the masticatingsection.

4. A machine according to claim 1 wherein said screw has an additionalthread formed therein and extending the length of the masticatingsection, said additional thread having a constant pitch.

5. A machine according to claim 1 wherein said screw has an additionalthread formed therein and extending the length of the masticatingsection, said additional thread also varying in pitch to both increaseand decrease within the length of the masticating section.

6. A machine according to claim 4 wherein two pairs of. grooves ofvarying depth are provided at the roots of said threads, a groove ateach `side of each thread, the groove on the lead side of one threadincreasing in depth as the groove on the trailing side of the adjacentthread decreases in depth so as to cause lateral flow of plastic acrossthe channel formed between said threads.

7. A machine according to claim 5 wherein two pairs of grooves ofvarying depth are provided at the roots of s'ald threads, a groove iateach side of each thread, the groove on the lead side of one threadincreasing in depth as the groove on the trailing side of the adjacentthread decreases 1n depth so as to cause lateral iiow of plastic acrossthe channel formed between said threads.

8. machine according to claim 1 wherein the pitch of said thread variescontinuously in accordance with a selected sinusoidal curve.

9. A machine according to claim 5 wherein the pitch of each of saidthreads varies continuously in accordance with selected sinusoidalcurves.

References Cited UNITED STATES PATENTS 2,556,276 6/ 1951 Henning.2,744,287 5/ 1956 Parshall et al. 2,765,490 10/1956 Zona. 3,123,860 3/1964 Vesilind. 3,300,810 1/1967 Gregory et al.

WILLIAM J. STEPHENSON, Primary Examiner.

